1. Field of the Invention
The present invention relates generally to measurement and testing for liquid analysis. More specifically, the present invention relates to the analysis of natural and synthetic oils for the purpose of detecting oil degradation and, further, for detecting the presence of contaminates such as soot, fuel and water. Oxidation and the presence of contaminates may be interpreted as an indication of the quality of the oil or any other non-polar liquid.
2. Description of the Related Art
Determining oil quality is a complex issue. Four methods of measuring and testing lubricating oil quality are generally accepted in the art: infrared spectroscopy, pH measurement, viscosity, and prediction of degradation.
Infrared spectroscopy utilizes a portion of the infrared region of the electromagnetic spectrum for analyzing organic compounds. For example, photon energies associated with the wavelength range of 2,500 to 16,000 nm, which corresponds to a frequency of approximately 1.9×1013 to 1.2×1014 Hz, are not large enough to excite electrons. These photon energies may, however, induce vibrational excitation of covalently bonded atoms and groups. As molecules experience a variety of vibrational motions characteristic of their component atoms, virtually all organic compounds will absorb infrared radiation that corresponds (in energy) to these vibrations. Infrared spectrometers obtain absorption spectra of compounds that are a unique reflection of their molecular structure.
While infrared spectroscopy offers the advantage of determining a number of oil qualities—including and in addition to lubricity—this methodology requires the removal of an oil sample from a source (e.g., removing oil from the motor of an automobile) and placing the oil sample in an infrared spectrometer. In addition to being expensive, this methodology is not conducive to ‘on-the-fly’ testing. Absent infrared spectrometers being introduced as standard equipment in automobiles and other machines that utilize natural and synthetic oils, infrared spectroscopy cannot be utilized to provide instantaneous indications of oil quality and/or that oil needs to be changed.
The second method of measuring and testing lubricating oil quality—pH measurement—is a logarithmic measurement of the number of moles of hydrogen ions per liter of solution. Thus, pH measures the hydrogen ion concentration in a liquid solution such as natural and synthetic oils. Low pH values (e.g., 0) indicate acidity and high pH values (e.g., 14) indicate causticity. Continual process monitoring and control of pH requires the use a specially prepared electrode (i.e., the measurement electrode). This specially prepared measurement electrode is designed to allow hydrogen ions in the solution to migrate through a selective barrier thereby producing a measurable potential difference proportional to the solution's pH.
While the pH of oil provides an indication of changes in acidity or causticity with regard to the presence (or absence) of certain acids, pH does not measure oil lubricating quality. Further, pH measurements do not determine if the oil has degraded due to foreign particles and contaminants such as water or metal particulate. Additionally, pH measurements can be skewed by the presence of volatile acids that evaporate over time at certain operating temperatures. The presence and/or subsequent evaporation of those acids can provide a false and/or inconsistent pH reading that is not relative to the actual quality of the oil being measured. A pH sensor apparatus, too, is expensive and not particularly suited for the environment of the oil pan of an internal combustion engine.
The third measurement methodology—prediction of degradation—is simple to a fault. Based on the knowledge that oil maintains a particular quality over a period of time, the mileage traversed since a previous oil change in a vehicle can be utilized to inform the owner of the vehicle that it is time to replace the oil. The timing of the indicia of replacement (e.g., the activation of a dashboard warning light) is based on the prediction of degradation and that the oil is no longer providing particular performance guarantees as governed by the quality of the oil.
This methodology, however, does not take into account the various qualities or quantities of oil that may be used in a particular vehicle. This methodology further fails to account for the particularities of the engine operating environment (e.g., engine wear independent of the oil quality) in addition actual driving conditions (e.g., city or highway, summer or winter, and so forth). This methodology, in addition to its overall inaccuracy, provides no qualitative or quantitative information regarding oil condition in that the indicia of the need for oil replacement is purely binary (i.e., time-to-change or not time-to-change).
A fourth technique measures the viscosity of the oil. As a result of the oxidation process, oil becomes thicker. A thickening of the oil can be an indication of the extent of oil breakdown.
While viscosity can provide an indication of oil wear, viscosity is dependent on the temperature and the particular viscosity improvement package added to the oil. For a viscosity measurement to provide an accurate measurement of oil quality, the temperature and type of viscosity improvement package must be known. The presence of contaminates will further increase or decrease the viscosity of a particular oil sample thereby hampering measurement.
As previously noted, base engine oils are non-polar and provide near-zero conductivity when clean. As the oil wears, the oil slowly begins to oxidize and exponentially increase in polarity as is shown in FIG. 1. FIG. 1 illustrates oil that, initially, is clean and non-polar. In the presence of O2 and heat, the oil begins to degrade. This application of O2 and heat would occur through, for example, the normal and ongoing use of the oil in an automobile.
This partially degraded oil, as also shown in FIG. 1, begins to take on polar characteristics. Through the continued application of O2 and heat, the oil becomes even more degraded and takes on even grater polar characteristics as further shown in FIG. 1. Increased polarity causes the oil to change is dielectric constant, which in turn leads to increased capacitance.
Most fully formulated oils incorporate deposit control additives, anti-wear and extreme pressure additives, corrosion inhibitors, and antioxidants. These protective additives generally consist of a polar salt head and a nonpolar hydrocarbon tail to trap harmful byproducts of oil wear. Depending on the exact concentration of various additives, the oil's dielectric constant and conductivity will vary according to the manufacturer, batch, and base type.
Clean and fully formulated oil typically has a higher starting capacitance than that of worn base oil. Because of this higher capacitance, electrical measurement of clean oil actually measures the additive package and not the properties of the base oil. Oil deterioration also results in a decrease of additives. As the dielectric constant of the oil becomes greater than that of the additives in the oil, useful direct oil analysis becomes difficult if not impossible.
While a variety of means are known in the art to measure oil pressure, there is a general lack of means to accurately and effectively measure oil quality. Those sensors that do exist often encounter the aforementioned problem of differentiating increases in oil dielectric constant versus presence and quality of oil additives. Measurement of oil quality is important in that the oil in a vehicle or other mechanical device needs to be changed when the oil loses its lubricity or becomes populated with contaminates.
There is a general need in the art for means to measure oil quality notwithstanding changes in oil dielectric constants. There is a further need in the art for monitoring an array of sensors in the oil thereby providing an early warning of degradation due to oxidation and detecting excess soot and water.